This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. To gain insight in the metabolism of the toxic element lead (Pb) in the human organism, detailed studies on the storage sites of Pb as well as on its chemical bonding in human bone and cartilage are essential. Therefore, during the last 4 years the distribution of Pb in calcified tissue has been extensively studied and revealed a very localized accumulation of Pb in small zones (about 15 [unreadable]m) of high metabolic activities in the cartilage area. The next step will be the determination of the chemical bonding of Pb in human calcified tissue, which should be performed within the proposed micro XANES experiment at SSRL. Since it is known from literature and our micro XRF studies, that Pb is on the trace element level in human calcified tissue these measurements are only possible using synchrotron radiation. The highest possible flux (in the range of E9 ph/s) from a wiggler beamline (BL 9-3) combined with modern X-ray optics (capillaries) and large area detectors will be mandatory to perform the measurements with sufficient counting statistics. Furthermore it will be possible to determine the chemical speciation of Pb in bone and cartilage with high spatial resolution ( about 15[unreadable]m). The expected results will allow to determine whether there are differences or similarities in the storage of Pb in bone and cartilage. These findings could help to explain why Pb is predominantly stored in calcification fronts of bone- and cartilage tissue. The knowledge on how Pb is stored in different tissue might also hold information on the its large biological half life (up to 20 years) in bone.